The present invention relates to a conveyor device for conveying an object to be processed or conveyed, such as a semiconductor wafer, in a processing station.
During the processing of a semiconductor wafer, an object to be processed could be subjected to preprocessing before a prescribed processing is performed on it in a certain processing station, or it could be subjected to postprocessing after a prescribed processing is performed. For example, before a thermal processing such as CVD is performed on a semiconductor wafer in a thermal processing station, the wafer is washed in hydrofluoric acid in order to prevent the formation of natural oxide layers on the wafer surfaces. In order to greatly increase the degrees of freedom of the processing in a thermal processing station with a built-in washing portion that enables such washing, the station is provided with a plurality of conveyor access opening portions and a plurality of conveyor means for conveying the wafers into and out of each of the conveyor access opening portions. For example, carriers for holding each different type of wafer are set in each conveyor access portion to enable the processing of different types of wafer.
Since the crystal of each wafer is orientated, orientation flats are formed in the wafers to align this crystal orientation. Wafers are held in a carrier with their orientation flats aligned, and the orientation flats are made to match a prescribed direction within the thermal processing furnace.
However, circumstances change if the conveyor route within the thermal processing station has different conveyor access openings. For example, the wafer conveyor routes are different between a case in which a wafer is taken by a first conveyor means from one conveyor access opening, that wafer is transferred to a second conveyor means and is conveyed thereby into a washing portion, the wafer is removed after it is washed from the washing portion by the second conveyor means, and then it is returned by the first conveyor means, and a case in which a wafer is taken by the second conveyor means from another conveyor access opening, that wafer is conveyed as is into the washing portion, the wafer is removed from the washing portion after it is washed, then it is transferred to the first conveyor means and is conveyed thereby into a processing furnace.
The positional relationships of the orientations of the conveyor means and the orientation flats can also change during the transfer of wafers between two or more conveyor means. For example, if a wafer is transferred directly from one conveyor means to another conveyor means, the orientation flat of the wafer will seem to have been rotated through 180.degree. from the individual viewpoints of the two conveyor means. This positional relationship of the orientation flat also varies with the number of times the wafer is transferred one conveyor means to another. Therefore, even if the orientation flats of all the wafers in the carriers have been aligned before processing, the orientations of some wafers may end up differing from the prescribed orientation within the thermal processing furnace, depending on which conveyor access opening the wafers are introduced through. In the current state of the art, an operator first sets each wafer-containing carrier in such a manner that the orientation of the wafers in the carrier corresponds to the conveyor access opening that is to be used, to ensure that wafers end up loaded within the thermal processing furnace in a prescribed orientation.
However, this preliminary setting of the wafers' orientation by the operator necessitates constant awareness of in which conveyor access opening each carrier is to be set. There is also the problem that, if the orientation of wafers within a carrier cannot be aligned with the prescribed orientation within the thermal processing furnace, the orientation of the wafers within that carrier will have to be changed later, which is troublesome to arrange.
Another problem occurs when wafers are to be conveyed accurately by a conveyor means to or from a cassette or a wafer boat that is used to load wafers into a thermal processing portion, or unload them therefrom, in which case it is necessary to ensure that the cassette or wafer boat is accurately aligned with the direction of motion of a holder arm. For example, if the orientation of a wafer boat should deviate from the direction of motion of the holder arm, the clearance of the holder arm with respect to the support posts of the wafer boat could be different on either side when the holder arm advances into the wafer boat, and the holder arm could mount onto the wafer boat and dislodge it, or the holder arm could come into contact with the support posts.
There are inevitably manufacturing errors in the dimensions of the various components of the mounting bases of the wafer boats or cassettes, and of the conveyor means, and assembly errors occur during the assembly of these components. For example, if a conveyor chamber is configured to act as a loadlock chamber, it has to be made of welded stainless steel plate of a thickness of 15 to 20 mm, to prevent distortion when it is evacuated. However, it is particularly difficult to reduce assembly errors with this sort of configuration, and there are always manufacturing errors in the components, so it can often happen that the orientation of the wafer container, such as a wafer boat, is not aligned with the direction of motion of the holder arm. Therefore, this method is conventionally limited to conveying within a restricted area, and conveying is by a multi-jointed holder arm which has a drive axis for each joint when a long stroke within a wide area is required.
Note that, when a simple holder arm that moves backward and forward in a straight line is used, it cannot be adapted to a large system with a long stroke, but, on the other hand, the use of a multi-jointed holder arm causes problems in that the construction of the conveyor means is extremely complicated and expensive.